It is known to prepare calcium nitrite by reacting calcium hydroxide with a gaseous mixture of nitrogen oxide gases. Mixtures of NO and NO.sub.2, such as are produced by the oxidation of ammonia, are used with a preferred mol ratio of NO:NO.sub.2 of at least about 1.0, especially about 1.0 or slightly above. Excess NO.sub.2 causes calcium nitrate to be coproduced in substantial quantities. For the desired enduses, this coproduct is undesirable.
There are several problems in applying the above reaction to commercial operation. First, gaseous emissions of nitrogen oxide gases are severely limited by environmental considerations. Second, because of the limited solubility of calcium hydroxide in water, the reaction thereof with nitrogen oxide gases is far more rate-limited than the corresponding reaction of sodium hydroxide to form sodium nitrite. Third, attempts to reproduce reported experiments for the production of calcium nitrite result in substantial calcium nitrate impurity levels.